The invention relates to a method for treating suspensions of solid particles in water. More precisely, the invention relates to a method for treating suspension of solid particles in water with a water-soluble polymer which has a comb structure and a specific composition.
Suspensions of solid particles in water include all types of sludge, tailings, or waste materials. The suspensions may result from mineral ores processes. They are for instance industrial sludge or tailings and all mine wash and waste products resulting from exploiting mines, such as, for example, coal mines, diamonds mines, phosphate mines, metal mines (alumina, platinum, iron, gold, copper, silver, etc. . . . ). Suspensions can also result from drilling mud or tailings derived from the treatment of oil sand. These suspensions of solid particles generally comprise organic and/or mineral particles such as for instance clays, sediments, sand, metal oxides, oil, etc. . . . , mixed with water.
The treatment of such tailings and other waste material has become a technical, environmental and public policy issue.
It is common practice to use synthetic or natural polymers such as coagulants and flocculants to separate the solids from the liquid.
For a long time, and even nowadays, mineral sludge produced by physical or chemical ore treatment methods were stored above ground in retention lagoons, ponds, dam or embankments in semi-liquid form. These large volumes of stored sludge therefore create a real hazard, especially if the dikes break.
Since the traditional storage solutions are obviously dangerous, more and more national regulations have been issued forbidding abandoning these zones. The regulations also call for an obligation to rehabilitate such sites, i.e. treating and consolidating, or requiring strict authorizations more and more difficult to fulfill.
The improvement of chemical and mechanical treatments of tailings or sludge is therefore a great challenge that needs to be addressed.
Various attempts were made in the past decades to increase the settling rate of the tailings in order to efficiently recycle water and reduce the volume of tailings ponds. The main physical treatments include centrifugation, filtration, electrophoresis and electro-coagulation.
On the other hand, chemical methods are emerging. They include process involving the addition of chemicals such as sodium silicate, organic flocculants, inorganic coagulants, oxidizing and reducing agents and more recently carbon dioxide.
In 1979-1980, Alsthom Atlantique and SNF (U.S. Pat. No. 4,347,140) developed a multistep flocculation system (super-flocculation) specifically designed for treating clay lagoons from phosphate production in Florida.
The treatment of suspensions was continuously studied in 1986 according to the method described in CA 1,273,888, then in 1994 in document WO 96/05146, in 2000 in document CA 2,407,869 and in 2004 in document CA 1,515,581.
In document CA 2 682 542, the process involves the addition of polymers modified by copolymerization and/or branching. Polymers having hydrophobic groups which have also been studied showed some improvement.
Despite great advances over the last 10 years, there is still a need to develop polymers that may enhance the speed and amount of water released from the tailings. Improvement of the physical characteristics of the produced sludge is also sought.